Bach was the son of Johann Ambrosius Bach, organist and town musician of Eisenach, German. The Bach family had produced many fine musicians during that time. J. S. Bach was orphaned at the age of 10 and went to live with his brother Johann Christopher at Ohrdruf where he had klavier and organ lessons. Most of Bach's compositions were composed for the organ. Bach studied the music of other composers by copying or arranging their scores, a habit he retained throughout his life. In this way, he became familiar with the methods of the foremost composers in France, Germany, Austria, and Italy, assimilating the best traits of each. He wrote primarily to meet the demands of the positions he held, and his works may be group accordingly: Arnstadt (1703-7), Muhlhausen (1707-8), and the court and chapel of the duke of Weimar (1708-17). At Cothen (1717-23), he worked as music director for a princely court, his duties did not include church music, he therefore composed works for keyboard or instrumental ensembles, as well as music for instruction and for domestic or court entertainment.
One of the larger musical structures in that period was the combination of Prelude and Fugue. Most of Bach's important compositions in this form date from the Weimar period, though a few written at Cothen and Leipzig.
What is polyphonic music?
Several simultaneous melody or instruments part are combined contrapuntally, as opposed to monophonic (single melody) or homophonic music (1 melodic line, the other parts acting as accompaniment). This type of music is very popular in the Baroque era or Renaissance period.
As an organist and devoted Lutheran, Bach care deeply about the chorale. He had written more than 170 organ chorales, he exhausted all known types in a constant search for artistic perfection. Bach's Orgelbuchlein (Little Organ Book) contains short chorale preludes, compiled at Weimar and Cothen with his pupils in mind. He compiled two "Little Notebooks" - collections of short keyboard pieces that taught technique and musicianship for his talented son Wilhelm Friedemann and for his second wife - Anna Magdalena. His two part Inventions and three-part Sinfonie are also pedagogical works.
Bach's also composed a large collection of pieces in the Harpsichord and Clavichord music. Most of these works were written while he was in Cothen, as well as in Leipzig. Undoubtedly the best known of Bach's works for keyboard is the double cycle of preludes and fugures that he titled Das Wohltemperirte Clavier (The Well-Tempered Keyboard, I and II, 1722 and ca. 1740).
Additionally, Bach also composed English suites and the French suites. Each set of the suite consists of the standard four dance movements - allemande, courante, sarabande, and gigue.
In the six Brandenburg Concertos, composed in 1721 and dedicated to the Margrave of Brandenburg, we see how fully Bach combined the Italian and German style. He adopted the three movement, fast-slow-fast order of the Italian concerto, as well as its triadic themes, steadily driving rhythms, and the ritornello form of the Allegro movements.
(Parts of this page quoted from Concise History of Western Music, written by Barbara Russano Hanning)